Pediatric oncology has a record of leadership in multidisciplinary patient care, multi-institutional. and interdisciplinary clinical research, and the integration of basic and clinical investigation. Continued progress in this direction is becoming more challenging, as the sophistication of clinical and biological research increases, and as cooperating disciplines become more specialized. It is essential that we train investigators interested in childhood cancer from different medical specialties in both clinical and biological research. The Division of Oncology of The Children's Hospital of Philadelphia (CHOP) has a much sought-after, board-certified three-year program of pediatric hematology-oncology fellowship training, with 50% percent of the fellows' time spent in either clinical or basic research. This program has trained 16 fellows since 1985, of whom 14 are in full-time academic positions conducting clinical and/or laboratory research. The Division and its affiliates at CHOP, the University of Pennsylvania, and the Wistar Institute have a strong record of leadership in clinical and basic science research. We propose here to train selected pediatric oncology fellows in both basic and clinical research, by adding enough supported time to their fellowships to allow completion of projects in both areas. We also propose to provide research training to residents and fellows from neurology, radiation oncology, surgery, and other specialties, who currently have few or no extended opportunities to conduct cancer research. The support provided would permit us to reduce the financial deterrents which now prevent many trainees from obtaining advanced research training. Through this program, we will train the next generation of clinical cancer researchers, whose work in bringing basic science to bear on clinical problems will advance progress against cancer in all age groups in the decades ahead.